Web Shell - file Private-i3lue.php

Hunt Hypothesis

This detection identifies adversaries establishing a persistent web shell named “Private-i3lue.php” to execute commands and maintain access within web-facing applications. Proactive hunting for this specific artifact in Azure Sentinel is critical because web shells often serve as an initial foothold for lateral movement, data exfiltration, or further compromise that may evade standard signature-based alerts.

YARA Rule

rule webshell_Private_i3lue {
	meta:
		description = "Web Shell - file Private-i3lue.php"
		license = "Detection Rule License 1.1 https://github.com/Neo23x0/signature-base/blob/master/LICENSE"
		author = "Florian Roth (Nextron Systems)"
		date = "2014/01/28"
		score = 70
		hash = "13f5c7a035ecce5f9f380967cf9d4e92"
		id = "393e738a-b4c2-5630-a55f-c3caee4ff75e"
	strings:
		$s8 = "case 15: $image .= \"\\21\\0\\"
	condition:
		all of them
}

Deployment Notes

This YARA rule can be deployed in the following contexts:

• Microsoft Defender for Endpoint — Custom indicators / advanced hunting
• Email Gateway — Attachment scanning
• File Share Monitoring — Periodic scanning of shared drives
• YARA CLI — Manual threat hunting on endpoints

This rule contains 1 string patterns in its detection logic.

• Source Rule

False Positive Guidance

Here are 5 specific false positive scenarios for the Web Shell - file Private-i3lue.php detection rule, along with suggested filters or exclusions:

• Scenario: Automated Backup Script Execution

  • Context: The enterprise uses a custom backup utility (e.g., Veeam Agent or a proprietary Python script) that generates temporary PHP files in the web root directory during nightly maintenance windows. The file Private-i3lue.php is created as part of this routine to log backup status before being deleted after 24 hours.
  • Filter/Exclusion: Exclude alerts where the process name matches the known backup service account (e.g., svc_backup) and the file creation timestamp falls within the maintenance window (01:00–03:00 UTC). Additionally, apply a filter to ignore files with a “temporary” flag in their metadata or those located specifically under C:\inetpub\wwwroot\temp\_.

• Scenario: CMS Plugin Update via Admin Panel

  • Context: The security team performs routine updates on the organization’s Content Management System (e.g., WordPress or Drupal) using a plugin manager. During an update, the system extracts Private-i3lue.php as part of a new module deployment package managed by the admin user (admin_user) via the web interface.
  • Filter/Exclusion: Create an exclusion rule for file creations originating from the specific IP address range of the internal administration subnet (e.g., 10.20.30.0/24). Furthermore, filter out alerts where the parent process is identified as the CMS web server worker thread (e.g., php-fpm or w3wp) and the file hash matches a known “good” signature stored in the asset inventory.

• **Scenario: Scheduled Reporting Job